Modified-edge-support heat treatment method of polyimide for crystalline, large-area, and self-standing ultrathin graphite films

Using a newly developed edge-support heat treatment method of polyimide, self-standing graphite thin films (GTFs) with a frame were prepared. The graphite basal plane in the GTF was oriented in the direction of the film surface, resulting in GTFs with high quality, large area, and a uniform thickness of 50-120 nm. The thickness distribution (3s) with an area of 25 mm x 25 mm and a thickness of 54 nm sample was 5.17 nm (measurement area 7.8 mm x 10.4 mm). The electric conductivity of a similarly prepared sample was 1.81 x 10(4) S/cm. The Young's modulus and ultimate tensile strength of a 60-nm-thick GTF were 1.02 x 10(2) and 5.34 GPa, respectively. Approximately 50 nm thick GTF samples were thinned by reactive ion etching using oxygen to fabricate a thickness between 10 and 20 nm. A film with an area of 10 mm x 10 mm and thickness of 16.7 nm exhibited a 3 sigma value of 1.80 nm which means that the thickness difference corresponds to 5 layers of graphite. The conductivity of a 16.2-nm-thick GTF was 1.79 x 10(4) S/cm. These results indicate that the etching proceeded uniformly. The proposed top-down method is an industrially superior method that overcomes the drawbacks of conventional bottom-up methods. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The study developed a new method of heat treatment for polyimide to prepare self-standing graphite thin films with high quality and uniform thickness. Reactive ion etching was used to thin the films and enhance their conductivity, showing promising results for industrial applications.